Water-salt phase transition of saline soils during evaporation

Along with the evaporation process, the solution in the pores of the saline soils will be vaporized and crystallized, and the two different phase transitions are interdependent. In order to reveal the water-salt phase change characteristics during evaporation, the vaporization and salt crystallization behaviors of the saline soils during evaporation are studied theoretically and experimentally. Firstly, starting with the thermodynamic theory, the theoretical expression for the initial crystallization radius is given by considering the interphase chemical potential balance and Young-Laplace equation, and the relationship among the initial crystallization radius, temperature and relative humidity is analyzed. Combined with the Van Genuchten soil-water characteristic curve model, the salt dissolving-crystallization model under different states of pore solution concentration is established, and the influences of temperature and initial salt content on the salt-crystallization behavior are analyzed. Finally, the theoretical model is verified by the evaporation experiments with controlled temperature and initial salt content. The results show that the soil temperature and initial salt content have significant effects on the phase transition of water and salt in the pore solution during the process of ambient humidity reduction. When the soil temperature is higher, the water evaporation becomes faster and the liquid phase saturation is lower. With the increase of the initial salt content, the final liquid phase saturation decreases and the salt crystal volume ratio increases. The initial salt content also changes the humidity of salting out, and the generation of salt crystals will inhibit the evaporation of water.